Inexpensive small waste tote

For the few times a year we might need them, I carry one 7-gallon Aquatainer for hauling fresh water, another one well marked for grey water dumping, plus a 6-gallon Tote-N-Stor tank for black waste dumping. Filling the two waste haulers once is enough to add an extra day to our waste capacity, but if we need more, we're usually driving in and out often enough that multiple dump stops is not really an issue. The two waste tanks are small enough and light enough when full that we could even dump them into a standard toilet if necessary. We can go a week between dumps and rarely stay longer than that on sites without a sewer hookup, so the tanks don't get used much.